GUARANTEE METHOD FOR NONMETALLIC INCLUSION IN STEEL AND STEEL WITH GUARANTEED NONMETALLIC INCLUSION

摘要

PROBLEM TO BE SOLVED: To obtain a guarantee method which guarantees size of a maximum nonmetallic inclusion estimated to exist in a prescribed volume, by a method wherein extreme value of the size of a maximum nonmetallic inclusion in a reference area measured by being observed under a microscope is statistically processed by a normalization variable and a specific relational expression which is computed on the basis of it is used. SOLUTION: The extreme value of the size of a maximum nonmetallic inclusion in a reference area S0 measured by being observed under a microscope is statistically processed by using a normalization variable (y), and a nonmetallic inclusion in steel is guaranteed by a relational expression which is computed on the basis of it. Expression: (areamax )1/2 =ay+b, where (areamax )1/2 represents the square root of the area of the maximum nonmetallic inclusion, (y) represents a normalization variable, and (a) and (b) represent respective constants. At this time, the reference area A0 refers to an area per sample which is observed. When (n) pieces of samples are observed so as to be rearranged in the ascending order of the (areamax )1/2 , a normalization variable y1 with reference to the (areamax )1/2 of the size of a jth inclusion is expressed by an expression of y1 =-1n [-1n j/(n+1)}].